Breezy_Pete

Power to heaters of both oxygen sensors are the blue/red wires, originating at cabin fuse 9. Control is via the brown wire for precat sensor, and the brown/white for the post cat sensor. They go to engine ECU pin numbers 5 and 63 respectively.

Relays are further inboard. You have to take off the lower dashboard trim beneath the steering wheel to see, I think. There's a guide for another job on a Mk1 that includes instructions for removing that trim panel, here. not sure how similar it is on a mk2: You'll see the relay panel once that trim is removed.

Loud, smoky cars are antisocial, not cool.

None of the errors with E313, G85, or J492 seem to relate to any of the soft coding options in module 09, so I think these must relate to another control unit having its coding corrupted.

The coding structure for onboard supply control unit/ module 9 is as shown in this image. The derivation of the code for my partner's 2005 car is shown in red. Pick the options that apply to your car, add them all up, and try that.

Every hose connected to the intake manifold is a vacuum hose. Anything that isn't, isn't. So the PCV outlet hose, the EVAP purge valve outlet hose, the brake servo hose and the steel EGR outlet hose are all vacuum hoses, effectively. The ones connected to the air filter are just sources of clean, filtered air to EGR valve and valve cover.

Message me with reg number or VIN tomorrow, please.

One way valve is part of the servo vacuum hose, near the engine end of it. With engine cover off, it should be easy to see the entire hose end to end. Very unlikely that the fuel system has anything to do with the misfire. You may need some help from a garage?

Did you try driving the car during any of this testing? Sometimes you just need to start up and set off down the road before these systems reset themselves after a fault is rectified.

It will be in the instrument cluster coding, I believe. Module 17.

It should be quite difficult to remove from servo, unless you deplete the vacuum by pumping brake pedal a few times first. Suggests the one-way valve may have failed, possibly?

No, internal to each fan motor, the rectangles shown within the fan schematic symbols above.

The fans are wired in parallel with each other, so you should never see just one working unless there is a fault (motor brushes worn or sticking in holder), or a low speed internal resistor failed.

Listen for a hissing sound from deep in the dashboard central area when you switch on A/C. That might suggest refrigerant quantity has reduced due to leakage.

Check cabin fuse 14. It feeds the ECU an ignition switched supply, and the ECU relay coil. Look for loose or corroded contacts, as well as continuity of fuse element.

Don't bother, I think it's somewhere else. I can't understand what these instructions mean, or where the image is, but this is what workshop manual says:

Look under carpet over here (red marking):

Look on the left side under the carpet at the front of where the seat would be. Petrol tank cover is on the right side of the car. Outer, rear wiring is to ABS sensors.

Why not ask the service people that told you that it needs replacing?

Water box is a VW/Skoda term for the section that the windscreen area drains into, often referred to as the scuttle. Perhaps that wire runs within that area.

It would be pretty easy to swap the instrument cluster housing for an uncracked one. Window switch assembly too. Will almost certainly have some problems that are harder to sort than either of those, given its age. As will any 19+ year old car unless previous owner was a DIY enthusiast with good skills.

Wow, that's a while ago. Did it all work out in the end?

Probably normal. Do you know anyone with a similar age Octavia from your country to compare with? I think it's only a requirement to have a 'cruise control active' indication in some markets, so others don't have the lamp.

Fair enough, sounds like you know what you're doing.